EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: mackrc1 on July 16, 2015, 05:25:30 pm
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Hello!
Quick question on telephones, If I got an old analog phone and simply played out of a speaker the DTMF tones of the number I want to dial, will the exchange recognise the number and connect me? Or is there some digital wizardry going on nowadays?
Cheers
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It will work, but you might have to get a good close-coupling between speaker and microphone. Once-upon-a-time you could buy little keypads with built-in tone generator to do exactly what you're suggesting.
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No digital wizardry – DTMF tones are in-band (audio) signaling.
If the exchange accepts DTMF dialing, reproducing an audio file containing DTMF digits will be recognized exactly the same way as digits dialed in the phone’s keypad.
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Here in the U.S., the telephone company still recognizes the clicks from the old rotary dial phones. I would just plug it in and give it a try.
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The newer voip to analog units that you get with fiber don't read ticks anymore.
Ticks are ancient, rotary phones are in the museum.
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Best interface would have a 'valid dialtone' detection before sending of a phone# for connection. Easy to do manually for a person but circuit stuff needed to automated say for under micro control.
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Phone dialers was a thing in the US.
Pretty much it had memory for several phones that you could pre-program including calling card information and you just placed it on the microphone part of the handset and it will dial for you.
But I don't know where you'll find a payphone to use it, maybe they still have them at airports.
Edit: of course they did use DTMF to dial.
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Back in the Windows 98 days, there was actually an app used with email that plays phone numbers in DTMF, so you could just hold the phone up to the PC in order to automatically dial the number. It's a shame the digital phones used nowadays don't even try to emulate that, as manually dialing into conference calls (long session numbers and passcodes!) is a common source of frustration in offices.
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There is an App for that. Well at least for Android :)
But yeah I remember carrying my touchtone dialer everywhere way back then :)
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Yup it will always work as long as we have analog phone lines since its all audio.
The old pulse dialing method wont work trough the headset since for that the actual phone line is pulsed using a switch. In the old days these pulses ware directly used to increment a fancy decimal relay to route you to the next exchange.
The local landline provider here i think stopped using pulse dialing. As for voip it depends on what modem you got. A lot only accept DTMF, but some can work with pulse dialing.
Basically DTMF is still "current gen" technology in analog phone lines since nothing came to replace it.
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The old pulse dialing method wont work trough the headset since for that the actual phone line is pulsed using a switch.
Oh yes, with a bit of practice you could make calls by hitting the hook button with the right speed, even if your parents decided to put a lock on the dial. ::)
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Hello!
Quick question on telephones, If I got an old analog phone and simply played out of a speaker the DTMF tones of the number I want to dial, will the exchange recognise the number and connect me? Or is there some digital wizardry going on nowadays?
Cheers
Some phones may have filters that attenuate DTMF codes, but most phones should allow them.
'standard' electronic exchanges should allow both pulse and DTMF dialling. However, some newer exchanges that incorporate ADSL lines may not be able to work with older phones that don't filter out the higher frequency bands used for the ADSL signals.
There are also purely digital phone lines that require a special phone or digital encoder. Those types, though rare, might not work with a purely 'analogue' phone at all.
(Strictly speaking, we should call them 'linear' phones as digital audio signals are also analogues of the audio signal)
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Yeah a digital line would be something like ISDN. Those can fit 8 simultaneous phone calls down a single line. But even these phones have to send DTMF tones after the call has been dialed by some other magical digital hokus pokus in order to interact with old analog gear like small office exchanges or automated answering machines that listen for you pushing buttons during a call.